Solution:
2. What do you understand by water treatment? Explain why it is required?
Solution:
Raw water from any source contains suspended, dissolved, colloidal, and Biological or other impurities with water, without proper removal of these impurities from water, if water is supplied to the public, they will at the risk of their lives. For the portability of water, it should be free from unpleasant taste, odors and is called the treatment of water.
Requirement of water treatment:
- To remove the dissolved gases and color of water.
- To remove unpleasant and objectionable taste and odors from water.
- To make water fit for domestic use as cooking and washing.
- To remove corrosive property of water.
- To kill the pathogens harmful to human health.
- To make water potable for drinking purpose.
Solution:
The respective treatment required according to the nature of impurities in water is:
a) Screening: To remove large suspended particles that are present in raw water, screening is done. It is provided at the intake point .In this process water is passed through screens. Through this process, branches of tree, leaves, dead animal body, debris, pebbles, ice etc. can remove.
b) Sedimentation: The process in which water is retained in a tank or basin so that the suspended particles present in the water may settle down under the action of gravity is called sedimentation.
c) Filtration: Sedimentation with coagulation process removes large amount of suspended matters but it cannot remove very fine particles color , dissolved minerals, microsophic organism or bacteria .For removal of such impurities, water is passed through the thick layer of porous media beds which is called filtration.
4. What is screening? Describe briefly.
Solution:
5. What do you mean by sedimentation? What are the major types of sedimentation process? Explain.
Solution:
The process in which water is retained in a tank or basin so that the suspended particles present in the water may settle down under the action of gravity is called sedimentation in general sedimentation process are of two types.
a) Plain Sedimentation: The main purpose of plain sedimentation is to remove large amount of suspended solids present in raw water. Plain sedimentation is done after screening and before sedimentation with coagulation and is located near the filter units and in the case of variation of demand it can be used as the storage reservoir.
b) Sedimentation with Coagulation: The quantity of impurities removed by plain sedimentation is very low when raw water contains, very fine suspended particles of clay, sit and light colloid matter. The setting down and removal of such fine suspended particles is called sedimentation or by adding chemical the dissolved particles can be settled down to the bottom of tank. The process is generally called as sedimentation with coagulation.
6. Explain main principle of sedimentation.
Solution:
7. What are the design consideration of sedimentation tank? Explain briefly.
Solution:
Sedimentation tanks are designed to remove suspended solids from water or wastewater by gravity settling. The main design considerations are:
1. Surface overflow rate (SOR)
This is the most important criterion. It represents the flow per unit surface area of the tank. Lower SOR allows better settling of particles. Typical values depend on whether the tank is for water treatment or wastewater treatment.
2. Detention (retention) time
The time water remains in the tank should be sufficient for particles to settle. Commonly ranges from about 2–6 hours. Too short reduces efficiency; too long makes the tank uneconomical.
3. Tank depth
Adequate depth is needed to prevent resuspension of settled solids and to provide sludge storage. Usual depths range from 3 to 5 m.
4. Length-to-width ratio
For rectangular tanks, a ratio of about 3:1 to 5:1 is preferred to maintain uniform flow and minimize short-circuiting.
5. Inlet and outlet arrangements
Inlets should distribute flow evenly and reduce turbulence. Outlets (weirs or launders) should collect clarified water uniformly to avoid disturbing settled solids.
6. Weir loading rate
The flow per unit length of outlet weir should be controlled to prevent high velocities that can carry solids out with the effluent.
7. Sludge collection and removal
The tank must have proper sludge hoppers, scrapers, or mechanisms to collect and remove settled solids efficiently without disturbing the water column.
8. Provision for scum removal
Floating materials like oil or grease should be removed using skimmers or scum baffles.
9. Hydraulic considerations
Flow should be as laminar as possible, avoiding dead zones, eddies, and short-circuiting to ensure effective sedimentation.
These factors together ensure efficient, economical, and reliable performance of a sedimentation tank.
8. Why sedimentation with coagulation is necessary? Explain.
Sedimentation with coagulation is necessary because plain sedimentation alone cannot remove many of the impurities present in water—especially very fine and colloidal particles.
1. Limitation of plain sedimentation
Sedimentation works by gravity: heavier particles settle at the bottom.
But in natural water, a lot of impurities are:
· Very fine (clay, silt)
· Colloidal in size
· Electrically charged (usually negative)
These particles are so small and stable that they do not settle even if the water is kept undisturbed for a long time.
2. Role of coagulation
Coagulation involves adding chemicals like alum, ferric chloride, or polyaluminium chloride (PAC) to water. These chemicals:
· Neutralize the electrical charges on colloidal particles
· Destabilize the particles so they can come together
3. Formation of flocs
After charge neutralization, particles collide and stick together, forming larger, heavier aggregates called flocs.
4. Effective sedimentation
These flocs are:
· Bigger
· Heavier
· Easier to settle by gravity
So during sedimentation, they sink to the bottom efficiently.
5. Overall benefits
Sedimentation with coagulation:
· Removes fine suspended and colloidal matter
· Reduces turbidity and color
· Removes some bacteria and organic matter
· Improves the efficiency of filtration and disinfection that follow
9. What is filtration? Explain the types of fliter.
Filtration is a separation process used to remove insoluble solid particles from a liquid (or gas) by passing the mixture through a filtering medium (like filter paper, cloth, sand, etc.).
The solid that stays on the filter is called the residue, and the liquid that passes through is called the filtrate.
Types of Filtration
1. Gravity Filtration
o Filtration happens due to the force of gravity.
o Used when the solid is insoluble and coarse.
o Example: Separating sand from water using filter paper.
2. Vacuum (Suction) Filtration
o Uses a vacuum pump to speed up filtration.
o Best for fine solid particles and faster separation.
o Common in chemistry laboratories.
3. Hot Filtration
o Filtration carried out while the solution is hot.
o Prevents dissolved solids from crystallizing during filtration.
o Example: Removing insoluble impurities from a hot solution.
4. Cold Filtration
o Filtration done at low temperature.
o Used when crystals are already formed and need to be separated.
5. Sand Filtration
o Uses layers of sand and gravel as the filter.
o Commonly used in water purification plants.
6. Membrane Filtration
o Uses special semi-permeable membranes.
o Can remove very tiny particles, even microorganisms.
o Example: Reverse osmosis water filters.
10. Explain the major mechanisms in filter.
The respective treatment required according to the nature of impurities in water is:
a) Screening: To remove large suspended particles that are present in raw water, screening is done. It is provided at the intake point .In this process water is passed through screens. Through this process, branches of tree, leaves, dead animal body, debris, pebbles, ice etc. can remove.
b) Sedimentation: The process in which water is retained in a tank or basin so that the suspended particles present in the water may settle down under the action of gravity is called sedimentation.
c) Filtration: Sedimentation with coagulation process removes large amount of suspended matters but it cannot remove very fine particles color , dissolved minerals, microsophic organism or bacteria .For removal of such impurities, water is passed through the thick layer of porous media beds which is called filtration.
4. What is screening? Describe briefly.
Solution:
5. What do you mean by sedimentation? What are the major types of sedimentation process? Explain.
Solution:
The process in which water is retained in a tank or basin so that the suspended particles present in the water may settle down under the action of gravity is called sedimentation in general sedimentation process are of two types.
a) Plain Sedimentation: The main purpose of plain sedimentation is to remove large amount of suspended solids present in raw water. Plain sedimentation is done after screening and before sedimentation with coagulation and is located near the filter units and in the case of variation of demand it can be used as the storage reservoir.
b) Sedimentation with Coagulation: The quantity of impurities removed by plain sedimentation is very low when raw water contains, very fine suspended particles of clay, sit and light colloid matter. The setting down and removal of such fine suspended particles is called sedimentation or by adding chemical the dissolved particles can be settled down to the bottom of tank. The process is generally called as sedimentation with coagulation.
6. Explain main principle of sedimentation.
Solution:
7. What are the design consideration of sedimentation tank? Explain briefly.
Solution:
Sedimentation tanks are designed to remove suspended solids from water or wastewater by gravity settling. The main design considerations are:
1. Surface overflow rate (SOR)
This is the most important criterion. It represents the flow per unit surface area of the tank. Lower SOR allows better settling of particles. Typical values depend on whether the tank is for water treatment or wastewater treatment.
2. Detention (retention) time
The time water remains in the tank should be sufficient for particles to settle. Commonly ranges from about 2–6 hours. Too short reduces efficiency; too long makes the tank uneconomical.
3. Tank depth
Adequate depth is needed to prevent resuspension of settled solids and to provide sludge storage. Usual depths range from 3 to 5 m.
4. Length-to-width ratio
For rectangular tanks, a ratio of about 3:1 to 5:1 is preferred to maintain uniform flow and minimize short-circuiting.
5. Inlet and outlet arrangements
Inlets should distribute flow evenly and reduce turbulence. Outlets (weirs or launders) should collect clarified water uniformly to avoid disturbing settled solids.
6. Weir loading rate
The flow per unit length of outlet weir should be controlled to prevent high velocities that can carry solids out with the effluent.
7. Sludge collection and removal
The tank must have proper sludge hoppers, scrapers, or mechanisms to collect and remove settled solids efficiently without disturbing the water column.
8. Provision for scum removal
Floating materials like oil or grease should be removed using skimmers or scum baffles.
9. Hydraulic considerations
Flow should be as laminar as possible, avoiding dead zones, eddies, and short-circuiting to ensure effective sedimentation.
These factors together ensure efficient, economical, and reliable performance of a sedimentation tank.
8. Why sedimentation with coagulation is necessary? Explain.
Sedimentation with coagulation is necessary because plain sedimentation alone cannot remove many of the impurities present in water—especially very fine and colloidal particles.
1. Limitation of plain sedimentation
Sedimentation works by gravity: heavier particles settle at the bottom.
But in natural water, a lot of impurities are:
· Very fine (clay, silt)
· Colloidal in size
· Electrically charged (usually negative)
These particles are so small and stable that they do not settle even if the water is kept undisturbed for a long time.
2. Role of coagulation
Coagulation involves adding chemicals like alum, ferric chloride, or polyaluminium chloride (PAC) to water. These chemicals:
· Neutralize the electrical charges on colloidal particles
· Destabilize the particles so they can come together
3. Formation of flocs
After charge neutralization, particles collide and stick together, forming larger, heavier aggregates called flocs.
4. Effective sedimentation
These flocs are:
· Bigger
· Heavier
· Easier to settle by gravity
So during sedimentation, they sink to the bottom efficiently.
5. Overall benefits
Sedimentation with coagulation:
· Removes fine suspended and colloidal matter
· Reduces turbidity and color
· Removes some bacteria and organic matter
· Improves the efficiency of filtration and disinfection that follow
9. What is filtration? Explain the types of fliter.
Filtration is a separation process used to remove insoluble solid particles from a liquid (or gas) by passing the mixture through a filtering medium (like filter paper, cloth, sand, etc.).
The solid that stays on the filter is called the residue, and the liquid that passes through is called the filtrate.
Types of Filtration
1. Gravity Filtration
o Filtration happens due to the force of gravity.
o Used when the solid is insoluble and coarse.
o Example: Separating sand from water using filter paper.
2. Vacuum (Suction) Filtration
o Uses a vacuum pump to speed up filtration.
o Best for fine solid particles and faster separation.
o Common in chemistry laboratories.
3. Hot Filtration
o Filtration carried out while the solution is hot.
o Prevents dissolved solids from crystallizing during filtration.
o Example: Removing insoluble impurities from a hot solution.
4. Cold Filtration
o Filtration done at low temperature.
o Used when crystals are already formed and need to be separated.
5. Sand Filtration
o Uses layers of sand and gravel as the filter.
o Commonly used in water purification plants.
6. Membrane Filtration
o Uses special semi-permeable membranes.
o Can remove very tiny particles, even microorganisms.
o Example: Reverse osmosis water filters.
10. Explain the major mechanisms in filter.
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